A light modulation device that controls the scattering, reflection, and absorption of incident light allows for high contrast and high light-usage rate.
As a light modulation device that changes transmittance of light by applying an electric field, a liquid crystal panel having a liquid crystal layer as a light modulation layer sandwiched between a pair of substrates is well known. Liquid crystal panels, due to their very high contrast, are suitable as display panels.
However, some of the light entering the liquid crystal panel from a backlight is absorbed or reflected as it passes through the liquid crystal panel. In particular, in order to control the transmission of light, a liquid crystal panel is provided with polarizing plates, which allow through only polarization components of specific directions, respectively on surfaces of the pair of substrates opposite to the surfaces facing the liquid crystal layer. Thus, only a portion of the light that enters the liquid crystal panel passes through the polarizing plates, with a large portion of the light being absorbed by the polarizing plates. Thus, the loss of light due to absorption by the polarizing plates is a major factor in the decrease of light usage rate.
In recent years, light modulation devices that differ from liquid crystal panels and that do not require polarizing plates are being developed.
FIGS. 27(a) and 27(b) are cross-sectional views for describing the operational principles of a light modulation device disclosed in Patent Document 1; FIG. 27(a) is a cross-sectional view of a state in which light is absorbed, and FIG. 27(b) is a cross-sectional view of a state in which light is reflected.
As shown in FIGS. 27(a) and 27(b), the light modulation device disclosed in Patent Document 1 includes a light modulation cell 301 that has a pair of substrates 311 and 321, and a dielectric liquid 330 that is introduced between the pair of substrates 311 and 321 and that has plate-shaped particles 331 having a metallic color dispersed therein. Among the pair of substrates 311 and 321, one substrate 311 is provided with a uniformly planar electrode 312 that covers at least the entire pattern to be displayed. The other substrate 321 is provided with comb-shaped segment electrodes 322.
In the state shown in FIG. 27(a), the pattern electrode 312 is set at zero potential by a switch SW11. By connecting switches SW21, SW22, SW31, and SW32 connected to the segment electrodes 322 to the positive side of power sources E1 and E2 in this state, a voltage is applied from the power sources E1 and E2 to the segment electrodes 322.
An electric field in a direction perpendicular to the substrate 321 is formed, and the plate-shaped particles 331 are oriented in the direction perpendicular to the substrate 321. If light is radiated in this state to where the segment electrodes 322 are disposed, the incident light is mostly absorbed by the plate-shaped particles, and this results in black display.
On the other hand, as shown in FIG. 27(b), if the switch SW11 is open, and between segment electrodes 322 connected to the switches SW21 and SW22 corresponding to desired segments, the switch SW21 is connected to the positive side of the power source E1 and the switch SW22 is connected to the negative side of the power source E1, then an electric field parallel to the substrate 321 is formed between the segment electrodes 322 connected between the switches SW21 and SW22, and the plate-shaped particles 331 are parallel to the substrate 321.
As a result, the light that has entered where the segment electrodes 322 connected to the switches SW21 and SW22 are disposed are reflected by the plate-shaped particles 331, and thus, in areas where the segment electrodes 322 are connected to the switches SW21 and SW22, colors specific to the plate-shaped particles 331 are displayed.
FIGS. 28(a) and 28(b) are drawings for describing the operational principles of a light modulation device disclosed in Patent Document 2; FIG. 28(a) is a cross-sectional view of a state in which light is transmitted, and FIG. 28(b) is a cross-sectional view of a state in which light is reflected.
As shown in FIGS. 28(a) and 28(b), the light modulation device disclosed in Patent Document 2 includes: a plate 411 made of an insulating transparent material provided with an electrode 412; a substrate 421 provided with an electrode 422, the plate 411 and substrate 421 facing each other; and rib-shaped spacers 431 and 432 that maintain a constant gap between the plate 411 and the substrate 421.
The light modulation device disclosed in Patent Document 2 includes at least one compartment 401 for storing a particle suspension 442 in which a plurality of anisometric reflection particles 441 are suspended in an insulating fluid, and each compartment 401 is defined by the plate 411, the substrate 421, and the spacers 431 and 432.
The side faces of the respective spacers 431 and 432 are provided with electrodes 451 and 452, and the respective electrodes 451 and 452 are separated from the electrodes 412 and 422 provided on the plate 411 and the substrate 421 by passivation layers 461 and 462.
According to Patent Document 2, by setting the switch 471 connecting the electrode 412 to the electrode 422 in the closed state, setting the switch 472 connecting the spacer 431 and the spacer 432 in the open state, and applying a first voltage V1 greater than a saturation potential of the particle suspension 442, an electric field perpendicular to the plate 411 and the substrate 421 is formed. As a result, the anisometric reflective particles 441 in the compartment 401 are oriented in the direction perpendicular to the plate 411 and the substrate 421, and the particle suspension 442 becomes light-transmissive.
On the other hand, by setting the switch 471 that connects the electrode 412 to the electrode 422 in the open state and setting the switch 472 connecting the spacer 431 and the spacer 432 in the closed state, and applying a second voltage V2 greater than the saturation potential of the particle suspension 442, an electric field parallel to the plate 411 and the substrate 421 is applied. As a result, the anisometric reflective particles 441 in the compartment 401 are oriented in the direction parallel to the plate 411 and the substrate 421, and the particle suspension 442 becomes light-reflective.
In such a light modulation device, it is possible to perform display with excellent contrast by the reflection and absorption of light, and no polarizing plates are used, and thus, the light usage rate can be increased compared to a liquid crystal panel.